1. Field of the Invention
The present invention relates to a driving system. More specifically the present invention pertains to a driving system, wherein an output shaft of an internal combustion engine and a rotating shaft of a motor are mechanically linked with each other via a damper.
2. Description of the Related Art
Proposed driving systems include an internal combustion engine and two motors mounted on a hybrid vehicle (for example, disclosed in JAPANESE PATENT LAYING-OPEN GAZETTE No. 6-144020). In this proposed system, an output shaft of the internal combustion engine is linked with a rotating shaft of a first motor via a damper and a first clutch. The rotating shaft of the first motor is further linked via a second clutch with a drive shaft that mechanically connects with wheels. The drive shaft is also connected to a second motor. The first motor cranks or motors the internal combustion engine in the state that the first clutch is connected and the second clutch is released, thereby starting the internal combustion engine. After a start of the internal combustion engine, the power output from the internal combustion engine is used to enable the first motor to function as a generator and charge the battery in the above state of the clutches. Alternatively the power from the internal combustion engine is directly output to the drive shaft in the state that the second clutch is also in linkage, thereby driving the vehicle.
The crankshaft, which is the output shaft of the internal combustion engine, is generally a resilient body having a localized mass distribution and hence forms a vibrating system having the infinite degree of freedom. A torque variation due to a gas explosion or reciprocating motions of the piston in the internal combustion engine causes torsional vibrations of the crankshaft. When the natural frequency of the crankshaft coincides with the forcible frequency, a resonance occurs. An increase in amplitude of such torsional vibrations causes a foreign noise or abrasion of gears in the crankshaft system, and even leads to a fatigue destruction of the crankshaft in some cases. In order to avoid these troubles due to the torsional vibrations of the crankshaft, a variety of dampers have been proposed and used for reducing the amplitude of the torsional vibrations. The dampers having a significant effect on reduction of the amplitude of the torsional vibrations, however, require a special damping mechanism. This increases the required number of parts and makes the damper undesirably bulky. The small-sized simple dampers, on the other hand, have little effects.
The resonance occurs in many cases when the revolving speed of the crankshaft is not greater than an idle revolving speed, although it depends upon the type of the internal combustion engine. The conventional driving system, which motors the crankshaft of the internal combustion engine by the motor that is linked with the crankshaft via the damper, causes a resonance in the process of starting the internal combustion engine. A possible technique to solve this problem drives the motor by a specific control (vibration-regulating control). This technique, however, can not deal with an intentional operation of the driver, for example, an abrupt stop. Another possible technique uses a starter motor that motors the crankshaft of the internal combustion engine without the damper. This technique, however, increases the number of motors included in the driving system and makes the driving system undesirably bulky.
This problem arises in any range that causes a resonance, for example, in the process of stopping the internal combustion engine and during the rotation of the crankshaft by the motor while a fuel supply to the internal combustion engine is stopped.